Tobacco expansion process utilizing microwave energy

ABSTRACT

The filling capacity of tobacco is increased by exposing tobacco having a moisture content in excess of ten percent by weight impregnated with a volatile organic liquid to a source of microwave energy having a frequency of 300 MHz to 300 GHz whereby to volatilize the liquid and concomitantly expand the tobacco.

llnited States Patent 1191 Neumann et al.

TOBACCO EXPANSION PROCESS UTILIZING MICROWAVE ENERGY Inventors: Calvin L. Neumann, Clemmons;

Freddie W. Best, Winston-Salem, both of NC.

Reynolds Leasing Corporation, Jacksonville, Fla.

Filed: July 7, 1971 Appl. No.: 160,543

Assignee:

References Cited UNITED STATES PATENTS 11/1968 de la Burde l3l/l2l Aug. 13, 1974 3,409,028 11/1968 de la Burde 131/140 3,524,452 8/1970 Moser et a1. 131/140 P 3,575,178 4/1971 Stewart 131/140 P 3,599,645 8/1971 Johnson 131/140 P 3,683,937 8/1972 Fredrickson et a1 131/143 Primary Examiner-Melvin D. Rein Attorney, Agent, or Firm--Neuman, Williams, Anderson & Olson ABSTRACT The filling capacity of tobacco is increased by exposing tobacco having a moisture content in excess of ten percent by weight impregnated with a volatile organic liquid to a source of microwave energy having a frequency of 300 MHz to 3000112 whereby to volatilize the liquid and concomitantly expand the tobacco.

13 Claims, N0 Drawings TOBACCO EXPANSION PROCESS UTILIZING MICROWAVE ENERGY BACKGROUND OF THE INVENTION This invention relates to a process of treating tobacco and has for an object the provision of a process for increasing the filling capacity of a tobacco product.

Tobacco leaves when harvested contain a considerable quantity of water and during the normal tobacco l curing process this water is removed by drying, resulting in shrinkage of the leaf structure. In the usual pro cess of preparing tobacco for storage and subsequent cigar or cigarette manufacture, the tobacco regains very little, if any, of the shrinkage resulting from the drying step so that a significant loss in the filling capacity of the tobacco is the result. Thus, the cured tobacco has a bulk density which is in excess of that required for making satisfactory cigarettes or cigars. Also, during cutting of leaf or strips for making cut filler for cigarettes, frequently the shreds are laminated together to form hard, dense particles which occupy far less volume than the original shreds occupied. This is wasteful since these hard compacted shreds are not necessary in the tobacco to produce an article which is satisfactory for smoking.

Several procedures have been suggested in the prior art for increasing the normal filling capacity of tobacco products. For example, US. Pat. No. 3,409,023 describes a process in which tobacco stems are subjected to a source of microwave energy whereby to puff the stems. However, preliminary experimentation has shown that the process described in that patent has limitations since it is operable to puff stems only moderately and is not useful for puffing tobacco leaf which is the principal component of tobacco used for the manufacture of cigarettes, cigars and other smoking articles.

Accordingly, a further object of this invention is the provision of a process for puffing tobacco products involving the use of microwave energy in order to obtain a tobacco product having a high degree of filling capacity increase.

A further object of this invention is the provision of a process for puffing tobacco by use of microwave energy which is effective for puffing not only stems but also tobacco leaf in strip or shredded form.

A still further object of this invention is the provision of a process of puffing tobacco by microwave energy in which the production of undesired fines is essentially eliminated.

Further and additional objects of this invention will appear from the following description and the appended claims.

GENERAL DESCRIPTION OF THE INVENTION In accordance with one embodiment of this invention, a process is provided in which tobacco having a moisture content in excess of about percent by weight is impregnated with a relatively volatile organic liquid and thereafter exposed to a source of microwave energy under controlled conditions. This may be done in a batch process but is preferably accomplished by placing the moist and liquid impregnated tobacco product on a conveyor belt which carries it into proximity with a suitable microwave source. For example, the conveyor belt may be arranged so as to carry the impregnated tobacco into a magnetron microwave oven. There are on the commercial market a largenumber of microwave ovens which are suitable for or may be adapted to this purpose. Generally speaking, they are devices which generate microwaves having frequencies within the range of 300 MHz to 300 GHz, more particularly from about 600 MHZ to 30 GHz. The nature and intensity of the irradiation in the oven is such that heat is generated directly within the tobacco product in an amount sufficient to vaporize substantially all of the organic liquid within the tobacco particles in a very short period of time, usually less than about 1 minute. This vapor generation directly within the tobacco particles causes them to puff or expand whereby the desired increase in filling capacity is achieved.

The rate and degree of puffing depends upon a number of factors such as the amount of energy to which the impregnated tobacco is exposed which is in part a function of the power input to the microwave source, the length of time the tobacco is exposed to the source, the frequency of the microwave, the moisture content of the tobacco, and the kind and amount of volatile liquid impregnant in the tobacco at the time it is subjected to irradiation. Thus, the rate of advance of the conveyor belt through the irradiation zone is normally adjusted so as to expose the tobacco to the microwave energy for a period of a few seconds to less than about 1 minute. Longer periods of exposure may be necessary when using a relatively low power microwave source. However, the time and radiation intensity should not be so great that the tobacco becomes heated to the point where its normal flavor and aroma are adversely affected. Generally speaking, the range of power input to the microwave source which is useful in accordance with this invention is about 250 watts to about 30 kilowatts. While the microwave frequency may be within the range of 300 MHz to 300 GHZ in accordance with the process of this invention, it is usually preferred to employ a frequency within the range of about 600 MHz to about 30 GHz. Particularly useful frequencies are one of those which have been set aside for industrial application by the United States Federal Communications Commission, namely, 915 to 2450 MHz. The tobacco may be exposed to the radiant energy in any suitable type of microwave applicator. For example, it may pass directly through the microwave wave guide or it may be spaced on a conveyor at any convenient distance from the microwave power source in a continuous bulk microwave applicator. Such distance may vary from one to fifty centimeters, as may be convenient.

The tobacco to be treated in accordance with the process of this invention is preferably a cured tobacco and may be in the form of shreds, strips, leaves, stems, comminuted leaf or sheets of reconstituted tobacco. The process has particular utility in the puffing of cured and shredded tobacco leaf. The process is easy to control and excellent puffing results are obtained if tobacco shreds are used. Shreds are relatively easy to handle in continuous processes and the final puffed product of the process need not be subjected to shredding as may be necessary for cigarette manufacture. Shredding of the final product results in compressing the product which tends to destroy the ultimate objective of the process of this invention, namely, to expand the tobacco and eliminate compressed particles, as may have resulted from prior treatment including shredding. Any type of tobacco may be used in the practice of this invention and it is particularly useful for the processing of burley, flue-cured and Oriental (e.g., Turkish) tobaccos.

As is well known, there is no heat per se in the microwave radiation and the temperature to which the product being treated is raised is generated directly within the product per se by reason of the absorption of the microwave energy by the polar material, i.e., water present within the product. Accordingly, the temperature within the oven per se may vary over a wide range but is usually above about C., i.e., the freezing point of water but below the boiling point of the organic fluid at the pressure prevailing within the oven. Also, in operation, the irradiation of the tobacco product will ordinarily be carried out at atmospheric pressure, although there may be some situations in which moderately subatmospheric or moderately superatmospheric pressures would be desired. Care should be taken to avoid pressure which will inhibit the rapid vaporization of the volatile fluid within the tobacco by the heat generated during irradiation on account of the water present in the tobacco.

Burley and flue-cured tobaccos used in the manufacture of cigarettes ordinarily have a moisture content of about to percent by weight. In the practice of this invention, it is important that the moisture content of the tobacco when impregnated with the organic fluid and exposed to the source of microwave energy should be in excess of about 10 percent by weight and suitably as high as 100 percent by weight but preferably within the range of 10 to about 35 percent by weight of the tobacco (dry basis). If necessary, the desired moisture content may be achieved by any suitable procedure such as sprinkling, spraying, wet steam treatment or the like, as is known to those skilled in the art. The moisture in the product serves a dual purpose. In the first place, water in the liquid state is usually necessary to absorb the microwave energy applied by the oven to supply the heat for vaporizing the organic liquid with the concomitant expansion of the tobacco particles which are impregnated by it. In the second place, the moisture imparts plastic properties to the tobacco which permit the particles to puff or expand easily. The moisture content may under certain conditions exceed 100 percent by weight but this is generally not desired for continuous commerical operations. Tobacco having a moisture content above about 30 percent by weight has a tendency to be mushy or soggy and may be difficult to handle.

The volatile liquid employed for impregnating the tobacco is preferably one which is organic in nature, is chemically inert to the tobacco being treated and has a boiling point at atmospheric pressure between about 50 C. and +80 C. Compounds having atmospheric pressure boiling points above +80 C. do not provide good tobacco expansion and are difficult to remove completely from the tobacco after expansion without adversely affecting its flavor and aroma. Compounds having very low atmospheric pressure boiling points, i.e., below 50 C. are so volatile and fugitive that they do not remain in the liquid state in the tobacco in the desired concentration in the usually short time of impregnation and the time the tobacco is exposed to the source of microwave energy. Preferably, the atmospheric pressure boiling point of the liquid is between 15 C. and 50 C. Illustrative inert organic compounds are: aliphatic or cyclic ethers such as diisopropyl ether,

methyl butyl ether and furan; esters such as methyl formate, ethyl formate and methyl acetate; aliphatic hydrocarbons such as butane, pentane, isopentane, hexane and the corresponding unsaturated hydrocarbons; the cyclo aliphatic hydrocarbons such as cyclobutane, cyclohexane and cyclopentane; the halo-hydrocarbons ethyl chloride, propyl chloride, isopropyl chloride, secbutyl chloride, t-butyl chloride, methyl bromide, ethyl bromide, t-butyl bromide, methylene chloride, chloroform, carbon tetrachloride, ethylene dichloride, ethylidene chloride; and the fluorinated hydrocarbons represented by trichloromonofluoromethane, dichlorodifluoromethane, monochlorodifluoromethane, l,ldifluoroethane, chloropentafluoroethane, l ,l ,1- trichlorodifluoroethane and l ,2- dichlorotetrafluoroethane. The organic liquids that are preferred are the non-oxygenated compounds which are relatively non-polar in nature and are relatively or substantially immiscible in water. These preferred compounds as a group have relatively low specific heats and thus require only a low energy input to cause them to vaporize and expand within the tobacco. Preferred materials are the hydrocarbons and the halogenated hydrocarbons of the types indicated above. Mixtures of liquids of several compounds may also be used if the boiling points of the liquid mixtures are within the indicated temperature range. Such mixtures include the azeotropes such as the trichloromonofluoromethaneisopentane azeotrope.

The impregnation of the tobacco may be effected in any desired manner such as spraying, dipping, vapor treatment with subsequent condensation, and the like. Usually the necessary water is present in the tobacco at the time it is contacted with the organic impregnating liquid. However, if necessary, a part or all of the water may be added to the desired level before, during, or after impregnation with the volatile organic liquid. The tobacco is allowed to remain in the impregnating zone for a sufficient time for the liquid to thoroughly penetrate into the cellular structure of the tobacco. The time required for complete equilibration may vary from a few minutes to a few hours (e.g., 10 minutes to 5 hours) depending upon the compound or mixture used, the nature of the tobacco and the conditions of temperature and pressure.

The weight ratio of organic fluid to tobacco in the impregnated moist tobacco when introduced into the microwave irradiation zone may be varied over a wide range. Sufficient organic fluid should be present to give the desired puffing effect. In order to obtain significant tobacco expansion, the impregnated tobacco at the time of exposure to the microwave source is at least 10 parts by weight of organic fluid for each parts by weight of tobacco on a dry weight basis. Best results are achieved when the ratio is in excess of about 30 to 100, preferably in excess of l-to- 1. For reasons of economy in organic liquid recovery, liquid-tobacco ratios in excess of 5-to-l are not usually necessary or desirable.

During the exposure of the tobacco to the source of microwave energy, a substantial portion of the organic liquid is rapidly volatilized and escapes into the oven chamber. These vapors are removed from the oven in any suitable manner such as by application of a partial vacuum or by sweeping the oven with a gas which may or may not be prewarrned to a temperature up to about 100C. The removed vapors may then be condensed SPECIFIC EXAMPLES In carrying out the processes of the following examples, a Cryodry Model I-2LC Microwave Research System (oven) was employed as the energy source to expand the tobacco. It was operated at a frequency of 2450 i 50 MHZ. According to the specifications of the oven, there were nominally 2 kilowatts of useable power in the oven tunnel from a reported 2.5 kilowatt source. In each run a 5-gram sample of the impregnated tobacco was placed on a 100 X 50 millimeter evaporating dish, which was positioned about 50 millimeters below the wave guide, thereby leaving a sufficient opening for the vaporized liquids to escape from the tobacco during irradiation.

In order to measure the filling value or capacity of a cut filler, i.e., shredded, tobacco product as described in the following examples, a measuring device was used which is essentially composed of a 100 milliliter graduated cylinder having an internal diameter of about 25 millimeters and a piston having a diameter of about 24 millimeters and weighing about 802.5 grams slidably positioned in the cylinder. A 3-gram sample of tobacco was placed in the cylinder and the piston was positioned on it. The gravitational force exerted by the piston corresponded to a pressure of about 2.3 pounds per square inch. The filling value of the sample was the volume to which the 3-gram sample of tobacco in the cylinder was compressed after the weight of the piston had acted on it for a period of 3 minutes. This pressure corresponds closely to the pressure normally applied by the wrapping paper to tobacco in cigarettes. The moisture content of the tobacco affects the filling values determined by this method; therefore, comparative filling capacities of tobacco were made with treated tobacco and untreated tobacco controls having essentially the same moisture contents.

EXAMPLE 1 A sample of shredded flue-cured tobacco having a moisture content of 25 percent by weight was saturated with liquid F reon-l l (trichloromonofluoromethane) in the amount of 2 milliliters of Freon-l l per gram of tobacco (equivalent to about 4 grams Freon-l l per gram of tobacco, dry basis). Five grams of this impregnated tobacco sample was then exposed to the source of microwave energy in the microwave oven for a period of about 60 seconds. The tobacco was then removed from the oven and equilibrated at 60 percent relative humidity for 2 days. The filling value of the resulting product was found to be 39.0 milliliters per 3-gram sample as compared to a filling value of 12.5 milliliters per 3- gram sample for the untreated control having essentially the same final moisture content. This represents a filling value increase of about 212 percent.

EXAMPLE 2 Example 1 was repeated except that the tobacco had a-moisture content of 27 percent by weight and the impregnating liquid was pentane in the ratio of 2 milliliters of pentane per gram of tobacco (equivalent to about 1.7 grams of pentane per gram of tobacco, dry basis). The filling capacity of the equilibrated puffed tobacco product was 30.5 milliliters per 3-gram sample as compared to 14.9 milliliters per 3-gram sample for the untreated control equilibrated to essentially the same moisture content. This represented an increase in filling capacity of about percent.

EXAMPLE 3 In Table I there is presented data which show the effect on puffing by microwave of varying the distance from the end of the wave guide to the top of the tobacco sample in the Cryodry equipment above described. These data were obtained by puffing tobacco in accordance with the procedure outlined in Example 1 using S-gram samples of shredded tobacco having a moisture content of 26.3 percent and impregnated with 2.5 milliliters of Freon-l l per gram of tobacco by equilibration in a closed container for 4 hours. The filling values of the treated samples and the control were determined after exposure of each to 60 percent relative humidity for a period of 3 days and each represents the average of three determinations. It will be noted that the degree of expansion of the tobacco is roughly inversely proportional to the distance of the sample from the wave guide but that significant puffing occurs even though this distance is fairly substantial.

A second experiment was run to show the relationship between the moisture content of the tobacco and the degree of puffing by using the microwave oven above described. Again a shredded flue-cured tobacco was used in which the moisture content was adjusted to the values shown for each in Table II. Each sample was impregnated with 2.5 milliliters of Freon-ll per gram of moistened tobacco and equilibrated for 5 hours. The puffing conditions were essentially the same as those described in Example 1, the samples during irradiation being positioned at a distance of about 50 millimeters from the end of the wave guide. The results are shown in Table II.

Table II pacity is relatively less since the heating was discontinued before volatilization of a substantial amount of the Freon had taken place.

Sample Percent Moisture in Filling Percent Number Tobacco (dry basis) Value Increase Table IV Control-B 12.50 12.3

AB 12.32 12.9 4.9 Sam I E p e icrowavc xposurc Pcrccnt 28 14.50 14.9 21.1 3B I654 16,9 374 Number Time (seconds) Filling Vuluc lllLlLIlhC 413 18.80 19.4 57.7 58 22.02 21.7 76.4 B 1 .6 68 23.50 26.2 113.0 10 2D 78 24.21 27.5 123.6 20 813 27.62 25.3 105.7 40 30 98 28.82 24.9 102.4 SD 6D 60 22.6 76.6

The data in this Table indicate the importance of having a substantial amount of moisture in the impregnated tobacco before it is subjected to the microwave energy. It is the water in the sample which absorbs the microwave energy thereby raising the temperature to volatilize the organic liquid and puff the tobacco.

EXAMPLE 5 In order to demonstrate the effect of the amount of Freon-11 in the impregnated tobacco, an experiment was carried out, the data from which are shown in Table 111.

While several specific embodiments of this invention have been described in the foregoing, it will be appreciated that many modifications may be made without departing from the spirit and scope of the appended claims.

What is claimed is:

l. A process of increasing the filling capacity of shredded tobacco by at least percent which comprises exposing tobacco shreds having a moisture content of at least about 20 percent by weight and impregnated with at least about 0.45 part by weight of a vola- In this case the shredded tobacco had a moisture content of 28.38 percent and the amount of Freon employed for each sample is indicated as milliliters per gram of tobacco (wet basis) in the second volume and as grams per gram of tobacco (dry basis) in the third column of the Table. In this instance the filling capacity of the several examples was measured after final equilibration to the same value as the control, i.e., approximately 12.5 percent moisture content. It will be seen that best results were achieved when the weight ratio of Freon to tobacco on a dry basis was in excess of about 1.

EXAMPLE 6 Variations in exposure time were also studied in the equipment above identified. In the samples of this example, the tobacco contained 31.1 percent moisture and they were impregnated with 2.5 milliliters of Freon-l l per gram of tobacco with a four hour equilibration time. The general procedure above indicated was employed with the time exposure being indicated in the second column of Table IV. The filling capacities of the samples and the control were measured after reordering at 60 percent humidity for a period of 3 days. Here again it will be noted that there is :1 relationship be tween the exposure time and the percent increase in filling capacity. Where the times are short the filling catile organic liquid for each part by weight of said tobacco (dry basis) to a source of microwave energy having a frequency of between about 300 MHZ and 300 GHZ of sufficient intensity to cause rapid vaporization of said liquid and the concomitant expansion by at least 50 percent of said tobacco.

2. The process of claim 1 in which said liquid has an atmospheric pressure boiling point of between about 50 and C.

3. The process of claim 2 in which said boiling point is between about 15 and 50 C. and said liquid is selected from the group consisting of hydrocarbons and halogenated hydrocarbons.

4. The process of claim 1 in which the liquid is trichloromonofiuoromethane.

5. The process of claim 1 in which the liquid is pentane.

6. The process of claim 1 in which said frequency is between about 600 MHz and 30 6112.

7. The process of claim 1 in which said frequency is about 2450 MHz.

8. A process of increasing the filling capacity of shredded tobacco by at least 50 percent which comprises exposing tobacco shreds having a moisture content of between about 20 and 30 ercent by welght 1m= pregnuted with at least about 0.45 part by weight of 1m organic liquid per part by weight of tobacco (dry basis) to a source of microwave energy having a frequency of between about 300 MHz and 300 GHz of sufficient intensity to cause rapid vaporization of a major proportion of said liquid within a period of less than about 1 minute and the concomitant expansion by at least 50 percent of said tobacco shreds, said liquid being selected from the group consisting of hydrocarbons and halogenated hydrocarbons and having an atmospheric pressure boiling point between about and 50 C.

9. The process of claim 8 in which said liquid is a fluorohydrocarbon.

10. The process of claim 9 in which the fluorohydrocarbon is trichloromonofluoromethane.

11. A process of increasing the filling capacity of shredded tobacco by at least about 50 percent which comprises contacting tobacco shreds having a moisture content of between about and 30 percent by weight with a volatile organic liquid to provide a mixture of at least about 0.45 part by weight of said liquid for each part by weight of said tobacco shreds (dry basis) and exposing said mixture to a source of microwave energy having a frequency of between about 600 MHz and 30 GHz of sufficient intensity to cause rapid vaporization of said liquid within a period of less than about 1 minute and the concomitant expansion by at least 50 percent of said tobacco shreds.

12. A process of increasing the filling capacity of shredded tobacco by at least 50 percent which comprises impregnating tobacco shreds having a moisture content of between about 20 and 30 percent by weight with an organic liquid having an atmospheric pressure boiling point between about 50 and C. to provide a mixture of at least about 0.45 part by weight of liquid for each part by weight of tobacco (dry basis), introducing said mixture at a temperature below the boiling point of said fluid at a prevailing pressure into a microwave irradiation zone, and exposing said mixture to a source of microwave energy having a frequency of between about 600 MHz and 30 GHz of sufficient intensity to heat the water in the moist tobacco shreds'and to cause rapid vaporization of said liquid within a period of less than 1 minute and the concomitant expansion by at least 50 percent of said tobacco shreds.

13. The process of claim 12 in which said liquid is selected from the group of hydrocarbons and halogenated hydrocarbons and said boiling point is between about 15 and 50 C.

UNITED STATES PATENT OFFICE ECTION CERTIFlCATE OF COR August l3, 1974 Patent No. 3, 828,797 Dated Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby correctedas shown below:

Column 7, in. Table II, under the column headed "Sample Number",

second line, "AB'" should be 13 1111845, "volume" should be column Signed and sealed this 29th day of October 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents FORM PC4050 (0459) uscoMM-Dc scam-ps9 9 U 5. GUVERNMENT PRINTING OFFICE I 959 Q 366-33l 

2. The process of claim 1 in which said liquid has an atmospheric pressure boiling point of between about -50* and +80* C.
 3. The process of claim 2 in which said boiling point is between about 15* and 50* C. and said liquid is selected from the group consisting of hydrocarbons and halogenated hydrocarbons.
 4. The process of claim 1 in which the liquid is trichloromonofluoromethane.
 5. The process of claim 1 in which the liquid is pentane.
 6. The process of claim 1 in which said frequency is between about 600 MHz and 30 GHz.
 7. The process of claim 1 in which said frequency is about 2450 MHz.
 8. A process of increasing the filling capacity of shredded tobacco by at least 50 percent which comprises exposing tobacco shreds having a moisture content of between about 20 and 30 percent by weight impregnated with at least about 0.45 part by weight of an organic liquid per part by weight of tobacco (dry basis) to a source of microwave energy having a frequency of between about 300 MHz and 300 GHz of sufficient intensity to cause rapid vaporization of a major proportion of said liquid within a period of less than about 1 minute and the concomitant expansion by at least 50 percent of said tobacco shreds, said liquid being selected from the group consisting of hydrocarbons and halogenated hydrocarbons and having an atmospheric pressure boiling point between about 15* and 50* C.
 9. The process of claim 8 in which said liquid is a fluorohydrocarbon.
 10. The process of claim 9 in which the fluorohydrocarbon is trichloromonofluoromethane.
 11. A process of increasing the filling capacity of shredded tobacco by at least about 50 percent which comprises contacting tobacco shreds having a moisture content of between about 20 and 30 percent by weight with a volatile organic liquid to provide a mixture of at least about 0.45 part by weight of said liquid for each part by weight of said tobacco shreds (dry basis) and exposing said mixture to a source of microwave energy having a frequency of between about 600 MHz and 30 GHz of sufficient intensity to cause rapid vaporization of said liquid within a period of less than about 1 minuTe and the concomitant expansion by at least 50 percent of said tobacco shreds.
 12. A process of increasing the filling capacity of shredded tobacco by at least 50 percent which comprises impregnating tobacco shreds having a moisture content of between about 20 and 30 percent by weight with an organic liquid having an atmospheric pressure boiling point between about -50* and +80* C. to provide a mixture of at least about 0.45 part by weight of liquid for each part by weight of tobacco (dry basis), introducing said mixture at a temperature below the boiling point of said fluid at a prevailing pressure into a microwave irradiation zone, and exposing said mixture to a source of microwave energy having a frequency of between about 600 MHz and 30 GHz of sufficient intensity to heat the water in the moist tobacco shreds and to cause rapid vaporization of said liquid within a period of less than 1 minute and the concomitant expansion by at least 50 percent of said tobacco shreds.
 13. The process of claim 12 in which said liquid is selected from the group of hydrocarbons and halogenated hydrocarbons and said boiling point is between about 15* and 50* C. 